PLEASE make this a thing. I love using Noteflight but I will be forced to move to an offline software for the SOLE reason that Noteflight simply can not handle arranging for more than like, 6 instruments without becoming super laggy and buggy and impossible to deal with. I love this program and want to keep using it but when composing a 17+ instrument Big Band it becomes unbearable. I want this more than anything. Hurry up! You're losing customers

You can get this effect by using the overall time signature you need (such as 7/8) and then using beams to show the rhythmic groupings you want.

BUT it seems like you are talking specifically about how the time signature is displayed. For example, the one you mentioned would look like this:

3+2+2
8

This is not necessarily standard notation, but it is used sometimes. We would consider it but because you can already get the music to sound and read in the way you want, in the most standard way, it may not be a priority for us.

Please add more detail in the comments so we can understand what is more important to you: the way it’s displayed (we don’t already do this), or the ability to write the rhythms you want (we do already do this).